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OPTIMIZED TEMPERATURE COMPENSATION CIRCUIT APPLIED IN THE HIGH POWER AMPLIFIER

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention proposes a technique that provides optimized temperature compensation circuit applied in a high power amplifier. Three more temperature sensors are added to the amplifier with two sensors already in it. Sensor 3 is used to monitor water temperature from sensor 1 and sensor 5 locations. Cold plate temperature is close to linearity from sensor 2 to sensor 4. The cold plate temperature is also close to linearity. Four sensors are used instead of two in a linear configuration as there exists a temperature step change from sensor 5 to sensor 2.

Country

Undisclosed

Language

English (United States)

This text was extracted from a Microsoft Word document.

At least one non-text object (such as an image or picture) has been suppressed.

This is the abbreviated version, containing approximately
38% of the total text.

OPTIMIZED
TEMPERATURE COMPENSATION CIRCUIT APPLIED IN THE HIGH POWER AMPLIFIER

FIELD
OF INVENTION

The invention
generally relates to high power amplifier and more particularly to optimized temperature
compensation circuit applied in the high power amplifier.

BACKGROUND
OF THE INVENTION

In general, radio
frequency (RF) coil in magnetic resonance (MR) system outputs RF excitation which
generates magnetic (B1) field. Due to nonlinearity of RF amplifier, the actual
RF amplifier output have some distortion compared with the input, which results
in poor slice profile.

To improve
linearity, digital pre-distortion, analog pre-distortion, feedforward, and
backward, technologies are developed very quickly in recent years, especially,
in mobile communication systems. However, between MR system and communication
systems, MR has higher power than communication or mobile systems. High
dissipated power results in heat, which increases junction temperature and cold
plate temperature. Further, quiescent operating point floats away and the heat results
in gain decrease during period time of one pulse. If the quiescent operating
point does not resolve correctly, it poses a big challenge to all linearity
technologies.

As depicted from the above figure, the
output voltage is applied on all the modules of the final stages.

FIG. 2 depicts temperature on final
stages.

FIG. 2

As illustrated
in the above figure, two temperature sensors are mounted on TC1 and TC2
location, and the designer uses TC1 and TC2 average voltage to control gating-source
voltage. TC1 and TC2 are lower than temperature tested when the charge
sensitive amplifier (CSA) is in working state.

FIG. 3 depicts cold
plate temperature compensation.

FIG. 3

As illustrated
in the above figure, static current is maintained flat when the temperature
goes high in figure 3B while bias current goes up in figure 3A.

A conventional
technique uses a pair of thermistors which are connected in parallel to a
resistor of a value chosen with respect to the resistance of its associated
thermistor over a given temperature range. The technique controls the base
current over a range of ambient temperature variation. However, the bias
circuit is used for bias current and not for bias voltage.

Another
conventional technique uses a transistor package with the temperature
coefficient of the diode similar to the base to emitter junction temperature
coefficient of the associated transistor. The diode is closely spaced to its
associated transistor to provide a fast thermal response to maintain a stable
quiescent point and therefore provide thermal compensation. However, the
technique is used for integrated circuits (IC) but not for popular metal oxide semiconductor
field-effect transistor (MOSFET) or metal–semiconductor field effect transistor
(MESFET) and laterally diffused metal oxide sem...